A Simple Rule of Thumb for Diffusion on Transition-Metal Surfaces
ABSTRACT On the surface: Diffusion on transition-metal surfaces plays a key role in the transport of atomic and molecular species on catalytic surfaces. Density functional calculations show that there is a simple linear relation that allows the prediction of the diffusion barrier from the binding energy of the diffusing species on the respective metal surface. (Figure Presented).
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- "Therefore, a relatively fast diffusion of atomic oxygen may also be expected at the pressures and temperatures of interest here. This suggestion is also supported by a rule of thumb for diffusion of small atoms and molecules (like H, N, O, CO, NO) on metal surfaces, which predicts that the diffusion barrier is only about 0.12 times the adsorbate binding energy  "
ABSTRACT: This article describes the results of simulations of CO oxidation under low pressure conditions over a bimetallic Pt/Rh composite catalyst. The model is represented by a system of four differential–algebraic equations (DAEs) for the coverages of COads and Oads, on the two parts of the composite surface. Surface diffusion of both adsorbates is assumed to be fast. The experimentally observed synergetic effect concerning CO oxidation on a Rh surface partly covered by Pt monolayer islands is reproduced in the simulations. It is shown that this synergetic effect is due to the difference in the CO sticking coefficients on Pt and Rh surfaces. In addition, a new type of kinetic oscillations, namely “synergetic kinetic oscillations” are predicted by the simulations. These oscillations exist under conditions at which no oscillations can exist over Pt and Rh monometallic catalysts. The driving force of this new type of oscillations is connected to the large difference in binding energy of adsorbed oxygen atoms on Rh and Pt.Chemical Engineering Journal 02/2015; DOI:10.1016/j.cej.2015.02.050 · 4.32 Impact Factor
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ABSTRACT: Effects from adsorption of organic species on the surface of nanomaterials have been investigated. Exposure to organic contaminants during material processing, handling and environmental exposure is unavoidable during the manufacturing process of nanoscale materials. In addition, at the nanoscale, surface area to volume ratios increase and surface effects will have an increasing influence on the material properties. Experimentally measured electrical properties of gold nanowires and composition will be presented. The results indicated that C, C—O—C and C=O are adsorbed at the surface of the gold nanowires. These surface contaminants are believed to cause the increase in measured resistivity. A theoretical study was performed to investigate diffusion of these contaminants into the first surface layer, which may act as scattering mechanisms for current flow.Bulletin of the Polish Academy of Sciences, Technical Sciences 01/2007; 55. · 1.00 Impact Factor
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ABSTRACT: The role of Sb and Bi as surfactants in GaN growth is investigated using first-principles, periodic, self-consistent, density functional theory calculations. It is shown that N diffuses much slower than Ga on the Ga-rich GaN(0 0 0 1) surface. Surfactants such as Sb and Bi are considerably more mobile on this surface and they react with N to produce SbN and BiN intermediates. The diffusion of these intermediates on the Ga-rich GaN(0 0 0 1) surface is more facile than that of atomic N. Therefore, this intermediate-mediated transport mechanism would increase the effective diffusion length for N. As a result, Sb and Bi would improve step edge incorporation of N, leading to a reduction in the average surface roughness of the GaN samples. While the barrier for BiN diffusion on GaN(0 0 0 1) is only slightly lower than that of N, the calculated difference in the diffusion barriers of SbN and N on that surface is significant and this would cause the preferential sidewall facets to change from and to the vertical facets during lateral epitaxial overgrowth (LEO). Additional calculations show that Sb and Bi can act as surfactants on the surface too. However, the adsorption of all the species on is significantly weaker and the diffusion barriers of SbN and BiN are considerably higher compared to the GaN(0 0 0 1) surface. Consequently, the surfactant effect of Sb and Bi on the surface should be less pronounced compared to that on the GaN(0 0 0 1) surface.Journal of Crystal Growth 05/2007; 303(2-303):493-499. DOI:10.1016/j.jcrysgro.2007.01.012 · 1.69 Impact Factor